What is Charles’s law?

Charles Law

Interestingly enough , many different substances will behave exactly the same . The accepted explanation, James Clerk Maxwell raised around 1860, is the amount of space occupied by a gas purely it depends on the movement of molecules of gas. Under normal conditions, gas molecules are very far from their neighbors, and they are so small that their own volume is negligible. The law Charles is a gas law which states that gases expand when heated . The law is also known as thelaw of volumes .

What is Charles’s law?

Charles’s law is a law that tells us that when the amount of gas and pressure are kept constant , the ratio between the volume and the temperature will always have the same value .

  • What is Charles’s law?
  • History
  • Who proposed it
  • Statement of Charles’s Law
  • Formula
  • Experiments
  • Charles Law Applications
  • Importance
  • Examples

What is Charles’s law?

Charles’s law is one of the laws that is related to gases . It consists of the relationship that exists between the volume and the temperature of a certain amount of ideal gas, which is maintained at a constant pressure , by means of a constant of proportionality that is applied directly. Jacques Charles says that for a given sum of gas at constant pressure, as the temperature increases , the volume of the gas increases and as the temperature decreases , the volume of the gas decreases because the temperature is directly related to the energy of the movement of the gas molecules. So, for a certain amount of gas at a given pressure, there will be a higher speed of the molecules and a higher volume of the gas.


Charles’s Law was promulgated by Jacques Alexandre Charles, a renowned physicist and chemist of French origin. He was a professor of physics at the Conservatory of Arts and Crafts in Paris and with the Robert brothers, he built the first hydrogen-powered balloon. In 1787 he discovered the relationship that existed between the volume and the temperature of a gas that was under constant pressure. In 1802 he published his results, which became known as the “Charles and Gay-Lussac law . 

Who proposed it

The law takes its name from the French scientist and inventor Jacques Charles , who formulated it in the 1780s . The ironic part of the story is that Charles never published the work for which he is remembered, nor was he the first or the last to make this discovery. In fact, Guillaume Amontons had done the same kinds of experiments 100 years earlier, and it was Joseph Gay-Lussac in 1808 who made the definitive measurements and published results showing that every gas he tested obeyed this generalization.

Statement of Charles’s Law

Charles’s law establishes the following postulate: “At constant pressure , the volume that a gas sample occupies is directly proportional to the absolute temperatures that it supports”


According to the statement of the law, it can be expressed mathematically as follows:

1 T 2 = V 2 T 1

Where :

  • V = is used to represent Volume .
  • T = with this letter we represent the Temperature


On a cold day when you go out with a helium balloon the balloon falls apart. But when it is returned to the warm temperature , the balloon will return to its original shape . According to Charles’s law, this situation occurs because a gas , in this case helium, takes up more space when it is hot .

torch that is used to heat the air molecules inside the balloon, they move faster and disperse into space . The gas inside the balloon takes up more space , becoming less dense than the surrounding air. So the hot air inside the balloon rises due to its reduced density and makes the balloon float.

Pop-up thermometers work on Charles’s law. The thermometer is placed in the turkey and as the temperature increases and the turkey is cooked, the air in the thermometer is expanded to blow the plunger. The thermometer is calibrated so when it reaches the correct internal temperature , the lid of the thermometer pops off, indicating that the turkey is done.

When playing ping pong , the ball may be dented . If heated gently water while stirring and the ball is placed inside, the air inside the ball will expand as it is heated . The expanding air will push the dent and restore the roundness of the ball.

Charles Law Applications

Charles’s law can be used in the following applications:

  • Hot air balloons
  • Airbags
  • Pressure cooker.


Its importance lies in the fact that according to this law, gases expand when heated . Since the mass of the gas remains the same, the number of molecules per unit volume decreases as it is heated. In other words, it explains that hot air is less dense than cold air. This allows hot air balloons to rise, displacing cooler air in the atmosphere .


An example of Charles’s law already solved is the following:

  1. At 1.5 atmospheres and 25 ° C the volume of a gas is 600 cm3, if the pressure remains unchanged, what will the volume of the gas be at 20 ° C?

First step : the data given in the statement must be identified

1 = 1.5 atm (cte)

1 = 25 ° C

1 = 600 cm3

2 = 20 ° C

Second step:  know what the unknown is .

2 =?

Third step : we must solve for V 2 from the expression: V 1 · T 2 = V 2 · T 1 , thus:

2 = V 1 T 2

Fourth step:  transform ° C to K, as follows:

1 : K = ° C + 273 T 2 : K = ° C + 273

K = 25 + 273 = 298 K K = 20 + 273 = 293 K

Finally the values are substituted and the mathematical calculation is carried out .

2 = 600 cm 3 . 293K


The units (Kelvin) are canceled and the result is obtained :  2 = 589.93 cm 3

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